A transport network (TN) is used to carry data signals between a Radio Base Station (RBS), such as a NodeB or an eNodeB in 3G Long-Term Evolution (LTE) networks, and a Serving gateway (S-GVV) or Packet Data Network gateway (PDN-GW). A TN may be operated by a mobile network operator or by a third party transport provider. In the latter case there would be a Service Level Agreement, SLA, between the mobile and transport operators. With the rapid growth of digital data telecommunications following the introduction of 3G and 4G technology, TNs may frequently act as bottlenecks in the overall data transport process. Thus, various systems and methods have been proposed for improving or prioritising the way that data packets are transported by the bearers.
Service differentiation in the Radio Access Network (RAN) is one supplementary means for more efficiently handling high volumes of traffic. As a simple example, using service differentiation a higher bandwidth share can be provided for a premium service, and in this way the overall system performance can be improved. As another example, a heavy service such as p2p traffic, can be down-prioritized. Implementing such service differentiation methods requires integration into the Quality of Service (QoS) concept of LTE and Universal Mobile Telecommunications System (UMTS) technology. Details of the QoS concept for LTE can be found in the 3rd Generation Project Partnership (3GPP) Technical Specification TS 23.410. The main idea of this concept is that services with different requirements use different bearers. When a User Equipment (UE) attaches to the network a default-bearer is established (typically a best-effort service). However, if the UE invokes services having different QoS parameters then a dedicated bearer is established for each service. This is shown schematically in FIG. 1 for an LTE network architecture and traffic flows to/from the Application/Service layer 100 of a network—for example an IP Multimedia Subsystem (IMS) network. In FIG. 1, there are two Unicast Evolved Packet System (EPS) bearers each carrying traffic (i.e. data packets) in both directions: up-loaded traffic sent from a User Entity (UE) 102 with a Radio Bearer to an eNodeB 104, then with a S1 Bearer over a TN to a Serving Gateway (SGVV) 106, and then with a S5/S8 Bearer to a PDN-GW 108; and downloaded traffic in the reverse direction. A similar concept would apply with UMTS network architecture, details of which can be found in “3G Evolution, HSPA and LTE for Mobile Broadband” by Erik Dahlman, Sefan Parkvall, Johan Skold and Per Beming, Academic Press, Elseveir, ISBN 9780123745385. Service differentiation can be applied for both guaranteed bit-rate (GBR) and non-GBR traffic. The present disclosure is concerned only with non-GBR traffic.
FIG. 2 illustrates schematically in more detail the TN between the eNodeB 104 and the SGW 106 for the LTE example. This shows non-GBR data packets 120, that include packets 120a of a first bearer that relate to a first service provided by a first server 110, and packets 120b of a second bearer that relate to a second service provided by a second server 112. These data packets 120 are destined for user equipment such as UE 102 at the other side of the TN, where the arriving data packets are handled by a scheduler 114 and eNodeB 104. In addition to the non-GBR data packets, the TN also handles synchronization data and voice or other GBR traffic, as shown, and which has a strict priority above non-GBR traffic but which is not a concern of the present disclosure. The bandwidth available for sending the non-GBR traffic is shared between the bearers, but when there is congestion so that there is insufficient bandwidth for the TN to handle all the non-GBR traffic, then some data packets have to be dropped (shown as RED dropped packets in the Figure). The problem that arises is how to decide which non-GBR data packets should be dropped.
The bandwidth share of a Bearer cannot be controlled by the RAN, and so instead the sharing of bandwidth between the Bearers is currently mainly determined by the application level protocols, the service used and the user behaviour. In the current LTE solution for non-GBR traffic, as shown in FIG. 2, the traffic flow through the TN bottleneck is handled by the application level Transmission Control Protocol (TCP), which deals with congestion by setting the packet throughput according to the available bandwidth. If packet losses start to occur, then the TCP reduces the speed at which packets are delivered to the TN, while after successful packet forwarding the speed is increased gradually. However some greater level of control can be achieved using a sophisticated QoS solution in the TN where different types of non-GBR traffic are put into different queues and a differentiation scheme, such as Weighted Fair Queuing (WFQ) applied between these queues. This provides a degree of service differentiation between different service types of non-GBR traffic at an aggregate level, but not at a per-Bearer level.
For the High-Speed Downlink Packet Access (HSDPA) protocol there are two approaches to handling TN congestion. One is a rate-based solution where service differentiation can be applied. The problem with this solution is that it is not compatible with TCP congestion control. Therefore separate queues need to be implemented in the TN for HSDPA and LTE traffic. The other approach is an Active Queue Management (AQM) based congestion control (ABCC) for HSDPA. In this solution the application level TCP is notified about TN congestion and can then be used to resolve the TN congestion. This solution has the advantage in that it is essentially compatible with LTE, and can be used together with a Relative Bitrate (RBR) manager. However, there are architectural limitations, particularly as it requires communication between the nodes that are sharing the same TN bottleneck.
Considering congestion control and resource sharing from a more general point of view, there are three approaches that might be considered, in addition to the profiling based approach proposed herein. These include window-based solutions, rate-based solutions and hierarchical scheduling solutions. Briefly these are as follows.
In a window-based solution, control of resource sharing between bearers to provide a fair share for each bearer is a very difficult problem to implement. For example the LTE may use the TCP so that the bandwidth share of a Bearer is determined based on, e.g. the number of parallel TCP flows and the TCP RTT (round-trip delay time).
Rate-based solutions require use of a sophisticated (i.e. complex) algorithm to provide good performance (e.g. high utilization). In addition to this they require a shaping (i.e. buffering) capability to enforce the calculated bitrate and also signaling between the bitrate enforcement point and the congestion detection point. The HSDPA flow-control described above is an example of a rate-based solution.
In a Hierarchical scheduling solution, for example, a hierarchical scheduler is used in the edge node to emulate the TN bottleneck. For example, with a single TN bottleneck with 10 Mbps, then a 10 Mbps shaper is used in the edge node to avoid TN congestion. This solution supports only a single edge network and requires knowledge of the capacity of all potential TN bottleneck links and the TN topology.
Currently there is no common solution that provides efficient Bearer level service differentiation. The existing approaches all suffer from limitations as described above. Even if equal sharing between bearers, rather than service differentiation, was desired some mechanism would be needed to avoid very unfair situations arising. This unfairness is illustrated below. Currently, in a RAN TN-limited case, where resource sharing between users (bearers) is based on a per-TCP flow (as currently applied in LTE) very unfair bandwidth sharing between users can result. This unfairness can be demonstrated with reference to the illustration of FIG. 3.
The left-hand part of FIG. 3 illustrates how bandwidth is shared between two bearers in a RAN TN. One bearer is handling the traffic of a single aggressive user with several (in this example 4) parallel TCP flows, while another bearer is handling the traffic of a normal user with a single TCP flow. In this case, the aggressive user effectively throttles the TN by taking up the majority of the available bandwidth. In this Radio limited case a Uu scheduler guarantees the required fairness among bearers as each user is essentially assigned the proper bandwidth, meaning that the aggressive user's access rate is effectively limited. Just for comparison, the right-hand part of FIG. 3, illustrates what occurs in an Asymmetric Digital Subscriber Line (ADSL).
Note that for the case of internet access, with a large user aggregation the capacity of the aggregation is much greater than the peak rate of a user, and so this does not present a serious problem because many aggressive users would be needed. However, this situation may change with increasing access rates, giving rise to similar unfairness problems.
As FIG. 3 shows, without a service differentiation method the bandwidth share depends on the nature of the services being used (e.g. typically a p2p service uses many parallel TCP flows), which is in direct contrast to what the operator wants (i.e. to provide premium services with a higher bandwidth share than low priority services).
The present invention has been conceived with the foregoing in mind.